Jacks with damping means



March 8, 1966 DESMARCHELIER 3,238,850

JACKS WITH DAMPING MEANS 3 Sheets-Sheet 1 Filed Oct. 8, 1963 March 8,1966 Y. DESMARCHELIER 3,238,850

JACKS wxm DAMPING MEANS Filed Oct. 8, 1965 5 Sheetsh e 2 YVES lill iahah6y (PaAQ HTTORnEy March 8, 1963 Y. DESMARCHELIER 3,238,350

JACKS WITH DAMPING MEANS 5 Sheets-Sheet 3 Filed Oct. 8, 1963 FlG.4

FIGS

IIlVEnToR Yves Dggma fiflbRnEy United States Patent 12,1 3 1 Claim. (Cl.sir-sad Hitherto known hydraulic or pneumatic jacks frequently comprisea damping device which is intended to decelerate the movement of themoving part at the end of travel. These devices can be externally of thejacks, such as for example the counter-jacks, or internally of thejacks, such devices being either mechanical, pneumatic or hydraulic.

Known internal damping devices of pneumatic and hydraulic types consistessentially in creating on the face of the moving part which is notsubjected to driving pres sure, a counter-pressure intended to opposethe driving force and to decelerate the moving masses. In pneumaticjacks, this counter-pressure is created by the compression of the air ina damping chamber. This damping effect can be made regulatable byvariation of the flow of a permanent leakage establishing communicationbetween the damping chamber and the discharge.

However, this device has many disadvantages due particularly to thepresence of the permanent leakage. In fact, the flow of the latter mustbe sufficiently small to permit subjecting the air in the dampingchamber to increasing pressure without making the value of thecounterpressure such that it causes a rebound at the end of travel ofthe mobile part. The optimum value of flow for this permanent leakage,when it can be found, requires very fine adjustment. On the other hand,the value of this flow depends essentially on the law of the movement ofthe mobile part and is directly dependent on the moving masses and alsothe driving pressure. Therefore, it will be seen that regulation is notonly tricky but very unstable since it must be effected again for eachdiiferent value of the loads applied to the jack.

It should also be noted that if the damping efiect requires a smallvalue for the permanent leakage flow, this results in a considerablecounter-pressure producing considerable heating which results moreparticularly in rapid damage to the sealing elements.

The present invention makes it possible to overcome these disadvantages.It relates to a single-acting or double-lcting jack comprising anynumber or" cells, whose moving parts are adapted to be displaced withinclosed compartments under the action of a fluid under pressure, andcomprising means for creating a damping counterpressure on the faces ofthe mobile part not subjected to the working pressure, the mobile partitself creating the necessary counter-pressure for damping, andcharacterised in that the jack is provided with an outlet valveoperating at a pre-determined value of this counter-pressure. Thedamping device thus obtained is not only independent of the law of themovement of the mobile part but also independent of the moving massesand more particularly the loads applied to the jack.

A preferred form of embodiment of the invention will now be described,merely by way of example and in no limitative sense, with reference tothe accompanying drawings.

The following description relates to a pneumatic dou ble-acting jackwhose moving part is a piston slidable in a cylinder. Of course, thepresent invention is applicable to any jack of single-acting ordouble-acting type, single-cylinder or multi-cellular, hydraulic orpneumatic, and the moving part may be the cylinder or the piston.

ice

FIGURE 1 shows a diagrammatic view in axial section through adouble-acting pneumatic jack.

FIGURE 2 is an axial sectional view of a spring-loaded valve.

FIGURES 3, 4 and 5 show three different positions of the piston during ajack cycle.

The jack comprises:

A cylinder 1 whose ends 2, 3 each comprise an axial cavity 4, 5.

A piston 6 fast with a rod 7. The face of the piston opposite to that towhich the rod 7 is attached comprises a cylindrical portion 8 which isco-aXial and whose diameter and length are slightly less than those ofthe cavity 4. The piston rod '7 comprises in the vicinity of the pistona cylindrical portion 9 whose diameter and length are slightly less thanthose of the cavity 5.

A sealing element It) situated in a groove of the piston, providingsealing-tightness between the piston and the cylinder.

A sealing element 11 situated at the end of the cavity 5 effectingsealing-tightness between the rod 7 of the piston 6 and the outside.

Special sealing elements 12 situated respectively at the entrances ofthe cavities 4, 5 debouching into the cylinder, the form of theseelements being such that their lips open in the working sense andprovide sealing-tightness between the cylinder and the said cavities inthe damping sense. The terms working sense and damping sense will bedefined hereinafter.

Ducts 13, 14 intended for supplying and discharging fluid under pressurewhich are connected to a distributor not shown here and each comprisetwo branch ducts 15, 16. The ducts 15 each debouch into the cavities t,5. The ducts 16 each debouch into the cylinder ends 2, 3 by means ofspring-loaded valves represented diagrammatically at 17, and 18.

These spring-loaded valves are shown in detail in FIG- URE 2 andcomprise:

A body 19 screwed into the jack ends 3, 4 and which is locked by thelock-nut 27.

A closure member 21 held in closed position by a spring 22 the axialdisplacement of which is limited by an abutment 23 screwed into the body19 and comprising a sealing element 20.

Sealing elements 26, 28 ensure sealing-tightness of the inner chamber ofthe valves.

The invention will be better understood by considering a jack cycle,whose different phases are shown in FIG- URES 3, 4 and 5.

When the piston is in the condition of rest, with the rod withdrawn, adistributor not shown here sends compressed air into the duct 14.

The compressed air entering the cavity 4 and the lips of the sealingelement 12 descending, the pressure is exerted over the entire surfaceof the piston, which slides with a uniformly accelerated axial movementin the cylinder as illustrated in FIGURE 4.

The damping of the piston movement commences when the cylindricalportion 9 penetrates into the cavity 5, this damping being effected intwo phases:

(1) A phase of compression in an enclosed space wherein the aircontained in the space bounded by the face of the piston which is notsubjected to driving pressure and the cylinder end 2 cannot escape. Thisspace 24 is called the damping chamber in contrast to the space 25 whichis called the working chamber. The damping chamber is sealed on the onehand by the sealing element 12 whose lips bear against the cylindricalportion 9 under the action of the increasing pressure in the chamber 24,and by the valve 18 on the other hand. The spring 22 maintaining theclosure member 21 of the valve 18 is calibrated in such a manner thatthe opening of the valve connecting the chamber 24 with the atmosphereis effected at a specific value of the pressure prevailing in thedamping chamber. This value is such that it effects the dynamicequalisation of the driving pressure force and the damping force, thusannulling the acceleration of the piston and consequently all the movingmasses.

The advantage of compression in an enclosed space as has just beendescribed in contrast to damping obtained by a regulatable permanentleakage, is that it makes it possible to obtain rapidly a value ofdamping counterpressure which brings about dynamic equilibrium. At theend of this phase, the acceleration of the piston is nil.

It should be noted that in this phase of movement, the regulation for agiven jack depends only on the value of the feed pressure, and isindependent of the movement of the mobile member and of the loads whichare applied thereto.

(2) A phase of deceleration during which the pressure prevailing in thedamping chamber increases further, thus braking the moving masses. Theair contained in the damping chamber is connected with the atmosphere byway of the valve 18. The outlet flow is regulatable. Regulation iseffected by the abutment 23 screwed into the body 12 of the valve, whichlimits the axial displacement of the closure member 21.

The foregoing description shows the operation of a jack according to theinvention from the withdrawn rod position. It will be apparent that themethod of operation is the same when the starting position is the rodout position.

Of course, many modifications could be made to the form of embodimentwhich is given here purely by way of example, without departing from thescope of the present invention.

I claim:

A double-acting jack comprising a cylinder, a piston slidable in saidcylinder and with opposite end portions of said cylinder definingchambers within said cylinder, cylindrical portions respectivelyintegral with opposite faces of said piston and coaxial therewith, saidopposite end portions of said cylinder comprising means definingcylindrical cavities communicating respectively with said Cal chambers,said cylindrical portions being coaxial with said cylindrical cavities,each of said cylindrical cavities being adapted to receive therein arespective one of said cylindrical portions, two ducts for the supplyand discharge of fluid under pressure, a first pair of fluid passagemeans communicating with one of said ducts, a second pair of fluidpassage means communicating with the other of said ducts, one of thefluid passage means comprised in said first pair and in said second paircomprising valve means controlling the venting to the air of each saidone of said fluid passage means, each said one of said fluid passagemeans terminating in a respective one of said chambers, the other ofsaid fluid passage means comprised in said first pair and in said secondpair terminating in a respective one of said cylindrical cavities, eachsaid valve means comprising an axially displaceable closure member,abutment means for controlling the axial displacement of said closuremember, spring means urging said closure member into a position closinga respective one of said fluid passage means, one of said chambersreceiving fluid under pressure from one of said cylindrical cavities andcausing an axial movement of said piston efl'ective to cause anincreased fluid pressure in the other of said chambers, said springmeans being so calibrated that opening of said closure member takesplace in response to a predetermined value of said increased fluidpressure in said other of said chambers, said value being slightly lowerthan the value of the fluid pressure in said one of said chambers.

References Cited by the Examiner UNITED STATES PATENTS 2,382,457 8/1945Wertman et al. 91-394 2,704,996 3/1955 Peterson et al 9l-394 FOREIGNPATENTS 213,677 2/1961 Austria. 779,280 7/1957 Great Britain.

SAMUEL LEVINE, Primary Examiner.

FRED E. ENGELTHALER, Examiner.

